History of the Atom Scientists and Their Contribution

History of the Atom Scientists and Their Contribution to the Model of an Atom

Democritus (460 BC – 370 BC) • Proposed an Atomic Theory which states that all atoms are… • small • hard • indivisible and indestructible • made of a single material

John Dalton (1766 – 1844) In 1803, proposed an Atomic Theory which states: o All substances are made of atoms; atoms are small particles that cannot be created, divided, or destroyed. o Atoms of the same element are exactly alike o Atoms join with other atoms to make new substances

J. J. Thomson (1856 – 1940) Proved that an atom can be divided into smaller parts Discovered electrons In 1897, proposed the Plum Pudding Model atoms mostly consist of positively charged “pudding” with negatively charged “plums” (electrons) located throughout

Ernest Rutherford (1871 – 1937) In 1909, suggested the following characteristics of the atom: o It consists of a small core, or nucleus o This nucleus is made up of particles called protons o Most of the atom is actually empty space

Niels Bohr (1885 – 1962) The Bohr Model Suggests that electrons travel around the nucleus in orbits

Erwin Schrodinger (1887 -1961) • In 1926, explained that the exact location of an electron cannot be stated; • It is more accurate to view the electrons in regions called electron clouds

James Chadwick (1891 – 1974) Realized that the atomic mass of most elements was double the number of protons Discovered of the neutron in 1932

Progression of the Atomic Model - -- - + The structure of an atom, according to: Democritus James Ernest Erwin Neils Schrodinger Chadwick Rutherford Bohr& J. J. Thomson John Dalton